(a) Field of the Invention
The present invention relates to a plasma display panel (PDP) and, in particular, to a display electrode of the PDP.
(b) Description of the Related Art
A typical PDP is a display device in which vacuum ultraviolet rays from plasma generated by gas discharge excite phosphors to emit red (R), green (G), blue (B) visible light for producing an image. Such a PDP can achieve a large screen size over 60 inches while keeping its thickness within 10 cm. The PDP has features of excellent color reproduction and no distortion along its viewing angle. As compared to a liquid crystal display (LCD) device, the PDP has the advantage of a simple manufacturing process resulting in good productivity and low cost. As a result, the PDP has emerged as a promising flat display device for home and industry.
In a typical three-electrode type surface discharge PDP, address electrodes are formed on a rear substrate along a first direction. A dielectric layer is formed on the rear substrate to cover address electrodes. On top of the dielectric layer, barrier ribs positioned between the address electrodes are formed in a stripe pattern, and R, G and B phosphor layers are formed between the barrier ribs.
On a first surface of a front substrate facing the rear substrate. Display electrodes consisting of a pair of protrusion electrodes and a pair of bus electrodes are formed in a first direction crossing an address electrode. A dielectric layer and a protective layer in turn are formed on the entire front substrate covering the display electrodes.
Discharge cells are formed at locations where the address electrodes of the rear substrate cross a pair of the display electrodes of the front substrate.
Such a PDP adopts a driving method using memory characteristics to drive a large number of the discharge cells. A voltage difference over a certain value is necessary to start a discharge between a X electrode (or sustain electrode) and a Y electrode (or scan electrode), both forming a pair of the display electrodes. The certain voltage threshold is called the firing voltage Vf. When an address voltage Va is applied between the Y electrode and the address electrode, the discharge starts. The plasma is generated by the discharge in the discharge cell, and the electrons and ions in the plasma move toward the electrodes with the opposite polarity. As a result, electrical current flows.
Since the dielectric layer is coated on each electrode of an alternating current PDP, most of the moving space charge is deposited on the dielectric layer with the opposite polarity. Therefore, the net voltage difference across the gas between the Y electrode and the address electrode becomes smaller than the initial address voltage Va, and causes the discharge to be weak and disappear eventually. The dielectric layer on the Y electrode collects a relatively large amount of the ions, as compared to the dielectric layer on the X electrode. The accumulated charges on the dielectric layer over the X-Y electrodes are called the wall charge Qw. Also, the voltage across the space between the X-Y electrodes is called the wall voltage Vw.
When a discharge sustain voltage Vs is applied between the X electrode and the Y electrode successively, the discharge starts in the discharge cell when the sum Vs+Vw of the discharge sustain voltage Vs and the wall voltage Vw exceed the firing voltage Vf. Vacuum ultraviolet rays generated at this point excite the corresponding phosphor layer so that visible light is emitted and transmitted through the transparent frontal substrate.
In the case of no address discharge between the Y electrode and the address electrode (that is, the case that no address voltage Va is applied), however, there is no wall charge accumulated on the X-Y electrodes and therefore, no wall voltage. As a result, only the discharge sustain voltage Vs exists in the discharge cell between the X-Y electrodes. The resulting voltage is smaller than the firing voltage Vf so that the no discharge occurs in the gas between the X-Y electrodes.
In order to obtain the visible light as aforementioned, the conventional PDP requires many steps which are not efficient in terms of energy conversion. Therefore, a large consumption of electric power results, and consequently, the efficiency (a ratio of luminance to the power consumption) of the PDP is not as good as that of a cathode ray tube type of display device. Inside the PDP having the above-described structure, a face discharge occurs between the address electrode and the Y electrode, and requires a higher firing voltage as the discharge gap are increased. Also, as between the X electrode and the Y electrode, only a surface discharge occurs that is not efficient as compared to the face discharge.